class A BJT(bipolar junction transistor) amplifier.

[Den]

Hi all - I wonder if any of you guys can settle an argument.

I say that in a simple class A BJT amp, only NEGATIVE feedback is used, but
a friend reckons both negative AND positive feedback are used. I always
thought positive feedback would reduce the stability of the output and was
undesirable in an amplifier, unless it was being used as an oscillator.

Can anyone help?

Thanks in advance - Den.

 

[bushbadee]

Basically there is no such thing as positive or negitive feedback.
There is only feedback.
The phase angle of the feedback determines whether it acts as positive or
negitive feedback.
Positive phase feedback is generally used as a load correction in a power
supply.

I prefer what is called, Feed forward, to feedback

Feed forward does not effect the stability of an amplifier and corrects for
line variations.

feed forward takes a voltage dependent on the input voltage to correct
output variations to line fluctuations.
See Google for some of my papers on this subject.